The long term goals of this research program are to study the mechanisms responsible for establishing patterns of determined cell territories within early embryos. The specific objectives discussed in this proposal are to provide tissue specific probes and devise assays to understand how the earliest cell patterning events are controlled. Monoclonal antibody technology is being used to make probes for the earliest tissue-specific, biosynthetic events detectable in embryos. Monoclonal antibodies have already been produced which distinguish between neural and non- neural epithelium and antibodies directed against all dorsal mesoderm structures. These antibodies recognize tissue specific antigens prior to the times when organs can be distinguished morphologically, presumably they recognize early steps leading to specific pathways of determined cell types. Amphibian embryos are being used in the initial stages of these studies primarily because of the availability of material and the ease of micro- surgery and cell culturing techniques. However, these same antibodies and approaches will work with other species as well. The assays involve culturing different tissues surgically removed from gastrula through neurula stage embryos. The patterns of cells expressing the antigen of interest will be determined by immunohistological techniques. As assay is also being developed to determine and isolate the molecular components responsible for controlling the expression of one epithelial specific antigen, Epi 1, and to determine when these components are localized within the egg. Therefore, assays using tissue specific monoclonal antibodies can determine when patterns of both neural ectoderm and dorsal mesoderm cells are established, what tissue interactions are necessary, and how abnormal environmental cues or tissue interactions affect the patterns of cell expressing tissue specific antigens. Establishing probes and assays to study the mechanisms involved in organizing the embryonic body plan will enable researchers to test, in greater detail, the effects of various drugs and environmental perturbations on early development of mammals where early abnormalities are usually aborted.